1. Field of the Invention
This invention relates to trailing arm suspensions for wheeled vehicles for trailers, tractors, and other vehicles wherein the suspension includes a mechanism for fore or aft adjustment of the axle with respect to the vehicle frame in order to align the wheels.
2. State of the Prior Art
Proper axle alignment in road vehicles is important to prevent undue tire wear. Some common causes of improper wheel alignment in road vehicles include improper initial suspension system installation, accident damage, and impact or shock loads imposed on suspension components by potholes or other road irregularities.
Various wheel alignment adjustment mechanisms have been provided to permit adjustment of vehicle axles and wheels to proper alignment. For commercial vehicles, these mechanisms generally fall into two classes: (1) those which are adjustable as the suspension is being installed on the vehicle and then permanently fixed in the adjusted position by welding or the like, and (2) those which are adjustable at any time during and after installation, but which are held in the adjusted position mechanically.
The former classification of adjustment mechanisms is illustrated by U.S. Pat. No. 2,481,891 to Masser. In the Masser mechanism, elongated apertures in the form of slots are provided in the frame mounting brackets. A bolt is passed through the elongated apertures and through an aperture in the end of the trailing arm. The slots enable the trailing arm to be adjusted fore or aft relative to the vehicle frame. Plates are carried by the bolt and abut a raised lug on each side of the frame bracket. These plates are welded to the sides of the frame bracket after alignment, thereby fixing the adjustment mechanism in its aligned position. Once welded, the connection is no longer susceptible to tinkering or gradual loosening. If subsequent realignment is necessary, the welds must be removed.
The latter category includes more conventional adjustment mechanisms in suspension systems utilizing turn buckles, adjusting screws, eccentric pins, or the like to adjust the alignment of the axle relative to the frame. In each case, a clamp or equivalent device is used to lock the adjusting mechanism after the adjustment has been effected. These conventional systems have some undesirable characteristics: the mechanical locking devices were susceptible to loosening due to wear and usage with consequent deterioration of alignment; the mechanical locking devices were susceptible to the well-meaning tinkering of truck drivers or unqualified mechanics attempting alignment corrections with small hand tools by hit-or-miss methods; and, such mechanical locking devices generally require a plurality of parts thereby increasing the complexity, weight and cost of the suspension.
An improvement in a mechanically locked type of alignment mechanism can be seen in U.S. Pat. No. 4,595,216 issued to Ware on Jun. 17, 1986. In the Ware patent, a pair of plates on each side of the vehicle hanger bracket have mutual interengaging serrations to provide a plurality of discrete positions for alignment in the fore and aft directions. A secure, controlled adjustment of alignment is possible without the necessity of welding. One of the problems presented, however, is that alignment sometimes requires very minute adjustments which may be in a position other than the finite positions defined by the serrations.
It is desirable to provide an adjustment mechanism which will provide an infinite range of adjustment, but also provide an effective mechanism for realignment, if necessary, without destruction of parts, removing welds, etc. Such a mechanism should also be capable of producing a positive mechanical lock which is not susceptible to loosening and wear and tear, and not easily tampered with.